1. Technical Field
The present invention relates generally to switching in a packet switched network and, more specifically, to systems and methods that ensure that certain types of packets, such as packets carrying voice information, are switched smoothly and with an acceptable amount of jitter.
2. Background Art
At the backbone of most networks are switches interconnected via a communications medium. For example, Ethernet is a commonly used local area network scheme in which multiple stations are connected to a single shared serial data path. These stations communicate with a switch located between the shared data path and the stations connected to that path. The switch controls the communication of data packets on the network.
Packets may be used to transmit a variety of different types of information. One use for packets in a packet-switched network is to carry real-time voice information. The transfer of voice traffic over packet networks, and especially voice over IP (Internet Protocol) based networks, is rapidly gaining acceptance. A primary reason for this is that Voice over IP (VoIP) packet transfers may significantly reduce the per-minute cost of a voice connection relative to using traditional dedicated line connections.
One common concern in VoIP packet transfers is possible degradation in voice quality relative to traditional voice systems. Voice quality may be degraded for a number of reasons, including undue delay in transmitting packets through the switches in the network. Delays encountered in the transmission path of a packet can be characterized as variable delays and fixed delays. Fixed delays, such as the propagation time of a particular portion of the network, are about the same for every packet. Variable delays, or “jitter,” such as queuing time and media access time at a switch, may vary from one packet to the next. Due to jitter, one packet may be transmitted before a second packet, but yet received after the second packet.
To accommodate packet delays, a VoIP voice playing device may have a “playout” buffer for removing jitter from the packets. When the first packet in a conversation reaches the playout buffer, it is delayed an amount equal to the maximum allocated jitter. In this manner, no packet will be read out of the buffer while an earlier packet is still traversing the network.
Although the playout buffer assures that packets will not be read out-of-order, it also increases the total delay of the system because of the delay implemented by the buffer. If the total delay becomes too great, users will notice degradation in the quality of the voice playback.
Thus, there is a need in the art to manage and reduce packet delay for voice packets as the packets travel through switches in a network.